Conformational analysis of the methyl ester of alanine by gas electron diffraction and Ab initio geometry optimization

The gas electron diffraction data of the methyl ester of l-alanine were recorded at an approximate nozzle temperature of 80°C and analyzed with geometrical constraints taken from 4-21G ab initio gradient geometry refinements. The molecular intensities are consistent with a model for the most populated conformational state in which the NCCO torsion (τ) is syn-peri-planar and a bifurcated hydrogen bond exists between NH₂ and CO. Details of the intensity data make it impossible to rule out the presence of significant concentrations of a second conformer, (τ ⋍ + 150°), in contrast to the ab initio calculations which predict greater stability of the system at τ ⋍ −150° than +150°.